Desiccator for wet powder particles

ABSTRACT

A desiccator for wet powder particles of synthetic high polymer substance, the main construction of which is a long vertical cylinder having a material feeding inlet at a lower part on the peripheral wall thereof and an inverse conical section forming the bottom part of the cylinder, a high speed hot gas current inlet being provided at the vertical angle of the inverse conical section, and the top end of the cylinder being communicated to a cyclone for collecting the dried product through a conveying tube.

United States Patent Saito et al.

[ 1 Oct. 8, 1974 DESICCATOR FOR WET POWDER PARTICLES Inventors: ShigeruSaito; Tetsuya Watanabe;

Hideki Wakamori; Hideo Nakamura, all of Iwaki, Japan Kureha Kagaku KogyoKabushiki Kaisha, Tokyo-to, Japan Filed: Aug. 14, 1972 Appl. No.:280,205

Assignee:

Foreign Application Priority Data Aug. 18, 1971 Japan 46-62314 US. Cl34/10, 34/57 A, 432/15 Int. Cl. F26b 3/08 Field of Search 34/10, 57 A,57 R; 432/15,

References Cited UNITED STATES PATENTS 10/1949 Wachs 34/57 R Gishler etal. 34/10 2,903,800 9/1959 Skoglund 34/57 A X 3,066,017 11/1962 Jahnig3,263,338 8/1966 Gordon 3,273,257 9/1966 Johnson et al 3,399,462 9/1968Koch et al. 34/57 A Primary ExaminerWilliam F. ODea AssistantExaminer-William C. Anderson Attorney, Agent, or FirmWenderoth, Lind &Ponack [5 7 ABSTRACT A desiccator for wet powder particles of synthetichigh polymer substance, the main construction of which is a longvertical cylinder having a material feeding inlet at a lower part on theperipheral wall thereof and an inverse conical section forming thebottom part of the cylinder, a high speed hot gas current inlet beingprovided at the vertical angle of the inverse conical section, and thetop end of the cylinder being communicated to a cyclone for collectingthe dried product through a conveying tube.

2 Claims, 1 Drawing Figure DESICCATOR FOR WET POWDER PARTICLES Thisinvention relates to a desiccator, or a drying apparatus. Moreparticularly, it is concerned with a desiccator for wet powder particlesof synthetic high polymer substances.

lmportant problems in drying wet powder particles are the sufficientbreaking or division of agglomerated masses of wet powder particles intoindividual fine particles for enhancing the effect of the drying, anddispersion of these individual fine particles into a hot gas current fordesiccation. To meet both requirements, various proposals haveheretofore been made and put into practice. All these proposed devicesto solve the problem, however, are just a combination of a dryingmachine and a special device for crushing the mass of wet powderparticles and for dispersing individual fine powder particles into a gascurrent.

As one example, there has been employed a desiccating device, in which adryer is combined with mechanical means for dividing the mass of wetpowder particles such as, for instance, a cage mill, or other mechanicalexpedientprovided with a rotary body. While a remarkable effect ofdivision can be obtained from this type of apparatus, if the mass to bedivided is one that is highly agglomerative, there inevitably occurvarious problems such as notorious adherence of the wet, massive powderparticles to the crusher main body or to the inner peripheral portionthereof. Particularly, in the desiccation of synthetic high polymer,such adhered material not only mixes into the final product later on tolower the quality of the product, but also causes inflammation and fire,when the adhered material is exposed in a high temperature circumstancefor a long period of time, which is serious from the standpoint ofoperation and maintenance of the installation.

With a view to eliminating such defects and disadvantages in theconventional apparatus as mentioned in the foregoing, the presentinventors conducted a long series of studies and experiments, as theresult of which they have succeeded in building an improved desiccatingapparatus free from these disadvanges.

It is therefore the primary object of the present invention to providean improved type of desiccating apparatus useful for drying wet powderparticles of synthetic high polymer substance.

It is another object of the present invention to provide a desiccatorfor wet powder particles of synthetic high polymer, which is soconstructed that breaking up of agglomerated wet powder particles ofsynthetic high polymer substance as well as drying of individual wetpowder particles as crushed can be accomplished at a single step byutilizing high speed hot gas current.

It is still another object of the present invention to provide a methodfor drying wet powder particles of synthetic high polymer substance.

The foregoing objects and other objects of the present invention willbecome more apparent and understandable from the following descriptionof the invention, when read in conjunction with the accompanyingdrawing.

ln the drawing, the single FIGURE is a schematic structural diagram ofan embodiment of the present invention.

As seen from the FIGURE of the drawing, the desiccator according to thepresent invention is much simpler in its construction than that of theknown apparatus.

That is, the main part of the apparatus according to the presentinvention is a vertical cylinder 3, the bottom part 1 of which is in aninverse conical shape with an inlet 2 for high speed hot gas current atthe bottom center part thereof, and the upper part of which is connectedwith a conveying tube 5 for the desiccated product, which furthercommunicates to a cyclone 6 for collecting the dried product therein anda gas exhaust tube 7. The cylinder 3 is also provided at one position onits peripheral wall in the vicinity of the bottom part 1 with an inlet 4for feeding raw material to be desiccated.

Specifically, the cross-sectional area of the cylinder is necessarilyfrom 10 to times as large as that of the inlet 2 for high speed hot gascurrent, and the total length (or height) of the cylinder 3 should befrom 5 to 10 m long at least. The interior of the cylinder 3 need not beprovided with any special devices such as a crusher for agglomeratedmasses of wet powder particles or a sieve for screening such crushedpowder particles.

In the actual operation of the desiccator of the abovedescribedconstruction according to the present invention, air which has beenheated to and maintained at a temperature range of from 70 to 200C isblown into the cylinder 3 through the inlet 2 at the bottommost and ofthe cylinder as a high speed hot gas current of from 40 to m/sec.. Bythis high speed hot air current, agglomerates of the wet powderparticles of synthetic high polymer substance which is being fedcontinuously from the inlet 4 for feeding material are break up intoindividual fine particles, and these fine particles are perfectly driedin the course of their travel up through the cylinder 3 to the topthereof. The dried powder particles as the final product are thentransferred to the cyclone 6 through the conveying tube 5.

For the purpose of dividing and dispersing the wet powder particles ofsynthetic high polymer substance containing agglomerated particleswithin the cylinder, it is necessary to have a speed of the hot gascurrent through the outlet sufficient to blow the agglomerates upwardly,in other words, a speed of the hot gas current higher than the end speedof the agglomerates.

In practice, the size of the agglomerates is reduced to a certain extentwithin a feeding apparatus before the desiccator, and an averagediameter thereof is about 5 cm or less. The required speed of the hotgas current to blow this size of the particles upwardly is at least 30-m/sec..

Although it is desirable for the hot gas current to be the highestpossible in speed to exert much more breaking force against theagglomerates of the wet powder particles, most of the masses of powderparticles of synthetic high polymer can be sufficiently divided intoindividual particles at a current speed of 150 m/sec.. The hot gascurrent having an extremely high speed is obtained by an increasedoutlet pressure for a blower, and it is difficult to maintain constantthe current speed within the cylinder. A preferable speed of the hot gascurrent is therefore from 30 to 150 m/sec..

Moreover, the average speed of the hot gas current within the cylinderis determined by the particle size, specific gravity and shape of thematerial to be desiccated. It is necessary that the average currentspeed be chosen within a range between the end speed of the largestpowder particles in the material to be dried and the end speed plus 2m/sec.. If a current speed lower than this range is selected, any powderparticles having higher end speed than the current speed within thecylinder remain in the cylinder without being discharged therefrom. Onthe contrary, when a current speed higher than this range is selected,thepowder particles are discharged out of the cylinder withoutsufficiently dcssicated and without masses of powder particles beingcompletely broken up. Generally, in the case of synthetic high polymerparticles, effective dividing and drying of the powder particles can beattained at the selected current speed of from 1.5 to 5 m/sec..

Another important point in carrying out the present invention is thatthe cylinder should have a sharp expansion of the space at the apex ofthe inverse conical section constituting the inlet for high speed hotgas current into the cylinder main body where the current speed somewhatslows down, whereby violent turbulence occurs at the expanded portion ofthe cylinder to flush the inner surface of the inverse conical sectionso as to prevent the wet powder particles from adhering thereonto.

In this case, however, if the apex angle of the inverse conical sectionis too large, the wet powder particles fed from the material feedinginlet accumulate on this sloped bottom part and are difficult to flushby the turbulence caused by the high speed hot gas current passingthrough the center part of the cylinder with the consequence that theintended division of the masses of powder particles becomes difficult,hence continuous operation is impossible.

On the contrary, if the apex angle of the inverse conical section is toosmall, the defect of accumulation of the raw material on the slopedbottom part of the inverse conical section can be eliminated. However,there is caused another defect, namely that, since the expansion of thecylinder space from the apex angle of the inverse conical section, i.e.,the slope of the inverse conical section at its apex angle, is gentle,no turbulence occurs with the result that highly adhesive andagglomerative material will stick to this inclined surface of theinverse conical section.

As the result of various studies and experiments, it has been found outthat the apex angle of the inverse conical section is preferably in therange of 60 Next, for the wet powder particles of synthetic high polymersubstance to be effectively divided, dispersed and desiccated by thehigh speed hot gas current blown into the cylinder from the bottomthereof, the total length of the cylinder constitutes the thirdimportant point.

That is, when the powder particles including masses of particles areblown upwardly by the high speed hot gas current, it is necessary thatperfectly divided and dispersed particles are carried upward through thecylinder, while undivided masses lose their speed to drop downward. Inthis case, if the total length of the cylinder is too short, the massesof powder particles are also discharged from the cylinder by their owninertia imparted by high speed hot gas current before they lose theirspeed, and mix into the dried final product.

The height at which the blown-up masses lose their speed and dropdownward depends on the flow-rate of the high speed hot gas current, andsize, shape and weight of the agglomerated mass. As the result of study,

it has been found that, in order that there not be any agglomeratedmasses of the wet powder particles in the dried product, the totallength of the cylinder should be made greater than a value representedby a relationship of(0.05V 3m), where V is from to 150 meters and thenumerical value thereof corresponds to the numerical value of thedistance of the flow of the high speed hot gas current per second.

Furthermore, when the inlet for feeding the material to be dried is at avery high position on the cylinder, those particles having a lower endspeed than that of the current flow rate within the cylinder are blownupward as they are fed in from the position of the inlet, so that thespace below the feed inlet does not contribute to the drying operation,and the powder particles are discharged from the top of the cylinderwhile incompletely dried.

More concretely, length of the cylinder portion from the materialfeeding inlet to the outlet at the top thereof should be at least 3meters, and the position of the material feeding inlet on the peripheralwall of the cylinder should preferably be at a distance of from k tol/20 of the diameter of the cylinder but not exceeding l/ 10 of thetotal length of the cylinder from the bottom end thereof.

In the following, explanations are made as to continuously drying wetpowder particles of synthetic high polymer substance using thedesiccator according to the present invention.

First, hot air is blown into the cylinder 3 constituting the dryer mainbody from the hot gas current inlet 2 at the bottom thereof at a highspeed hot gas current of from to 150 m/sec.. Simultaneously, wet powderparticles of synthetic high polymer are continuously fed from thematerial feeding inlet 4. The powder particles thus fed into thecylinder 3 are dispersed and dried in the cylinder by the high speed hotgas current from the inlet 2. During the drying operation, agglomeratedmasses in the wet powder particles are also divided by this high speedhot gas current into individual fine particles.

Even among the masses of powder particles which have once been separatedand blown upwardly by-the high speed current, those masses which areinsufficiently divided and insufficiently dried drop downward again tobe repeatedly divided and dried by the hot gas current moving at anaverage speed of 1.5 to 5 m/sec. within the cylinder whereby only thefinely divided and dried powder particles are collected in the cyclone 6through the product conveying tube 5, and the desiccated product can betaken out therefrom as the final product.

The entrance speed of the high speed hot gas current as well as theaverage speed of the same within the cylinder according to the presentinvention may be varied. For the purpose of drying powder particles ofsynthetic high polymer, high speed hot gas current of 40 to 150 m/sec.and an average speed within the cylinder of 1.5 to 5 m/sec. caneffectively carry out the drying.

In order to enable skilled persons in the art to reduce the presentinvention to practice, the following actual examples are presented. Itshould be noted that these examples are illustrative only and are notintended to restrict the scope of the present invention.

EXAMPLE 1 M resin having a particle size range of from 44 to 1,000microns and a moisture content of 50% was fed at a rate of 18 kg/hr.into a desiccator constructed with a cylinder main body of 30 cm indiameter and 800 cm in height, the bottom part of which forms an inverseconical section having an apex angle of 60. The bottom center of theinverse conical section is provided with a high speed hot gas currentinlet of 5.5 cm in diameter. A material feeding inlet of 8 cm indiameter is provided at a position 10 cm away from the bottom end of thecylinder main body.

The drying operation was conducted under the following conditions.

ABS resin having particle size range of from 44 to 500 microns and amoisture content of 40% was fed at a rate of 40 kg/hr. into a desiccatorconstructed with a cylinder main body of 30 cm in diameter and 600 cm inheight, the bottom part of which forms an inverse conical section havinga the vertical angle of 60. The bottom center of the inverse conicalsection is provided with a high speed hot gas current inlet of 10 cm indiameter. A material feeding inlet of 8 cm in diameter is provided at aposition 10 cm away from an bottom end of the cylinder main body.

The drying operation was conducted under the following conditions.

Humidity of Air High Speed Hot 0.018 kg H O/kg D-air within CylinderWhat is claimed is:

1. A method for desiccating wet powder particles of synthetic highpolymer substance which comprises the steps of:

a. continuously feeding wet powder particles of synthetic high polymersubstance in a lateral direction into the lower portion of a defineddrying zone having a cylindrical cross section and a length in meters ofat least 0.05V 3, where V is from 30 to 150, and having an inverseconical section having an apex angle of from 50 to b. blowing into thedefined drying zone through the apex of the conical section a stream ofhigh speed hot gas at a temperature of from 70 to 200C at a flow rate offrom 30 to 150 m/sec., the value V being equal to the numerical value ofsaid flow rate, said stream further having a cross-section of from l/10to H the cross-sectional area of the cylindrical portion of the defineddrying zone for maintaining the average speed of the hot gas through thecylindrical portion at 1.5 to 5.0 m/sec.; and

c. withdrawing the dried particles and gas from the top of the defineddrying zone for sending them to a product collecting cyclone.

2. A method for desiccating wet powder particles of synthetic highpolymer substance which comprises the steps of:

a. continuously feeding wet powder particles containing agglomeratedmasses of the wet powder parti cles into a defined zone for drying; and

b. blowing into the defined drying zone a stream of high speed hot gasat a temperature of from 70 to 200C at a flowrate of 30 to m/sec. andhaving a cross-section from l/lO to l/ 100 the crosssectional area ofthe defined zone to cause fluidization of said powder particles withinthe defined drying zone for dividing the agglomerated masses intoindividual fine particles, dispersing and sufficiently drying the fineparticles within the drying zone;

the speed of the hot gas stream being sufficient to maintain the averagespeed of the hot gas through the defined drying zone at 1.5 to 5.0m/sec.

1. A method for desiccating wet powder particles of synthetic highpolymer substance which comprises the steps of: a. continuously feedingwet powder particles of synthetic high polymer substance in a lateraldirection into the lower portion of a defined drying zone having acylindrical cross section and a length in meters of at least 0.05V + 3,where V is from 30 to 150, and having an inverse conical section havingan apex angle of from 50 to 70*; b. blowing into the defined drying zonethrough the apex of the conical section a stream of high speed hot gasat a temperature of from 70 to 200*C at a flow rate of from 30 to 150m/sec., the value V being equal to the numerical value of said flowrate, said stream further having a cross-section of from 1/10 to 1/100the cross-sectional area of the cylindrical portion of the defineddrying zone for maintaining the average speed of the hot gas through thecylindrical portion at 1.5 to 5.0 m/sec.; and c. withdrawing the driedparticles and gas from the top of the defined drying zone for sendingthem to a product collecting cyclone.
 2. A method for desiccating wetpowder particles of synthetic high polymer substance which comprises thesteps of: a. continuously feeding wet powder particles containingagglomerated masses of the wet powder particles into a defined zone fordrying; and b. blowing into the defined drying zone a stream of highspeed hot gas at a temperature of from 70 to 200*C at a flowrate of 30to 150 m/sec. and having a cross-section from 1/10 to 1/100 thecross-sectional area of the defined zone to cause fluidization of saidpowder particles within the defined drying zone for dividing theagglomerated masses into individual fine particles, dispersing andsufficiently drying the fine particles within the drying zone; the speedof the hot gas stream being sufficient to maintain the average speed ofthe hot gas through the defined drying zone at 1.5 to 5.0 m/sec.